The Bay Area’s biotech industry is showing a middle-age problem: It’s soft in the middle.

With biotech giant Amgen Inc.’s $10 billion acquisition in October of South San Francisco’s Onyx Pharmaceuticals Inc., few companies are ready to fill the Goldilocks role of being just the right size — large enough to make a difference in drug development, but not so large that they are locally aloof.

The region’s biotech industry is dominated by large players — like Genentech Inc. and Gilead Sciences Inc. — and a growing community of early stage companies and startups.

In the middle? The most recognizable company there would be orphan drug developer San Rafael’s BioMarin Pharmaceutical Inc. which is the subject of continuous chatter around its sale to a large drug marketer in need of new products and revenue.

The dearth of mid-size companies risks hurting the long-term balance of the Bay Area’s biotech ecosystem, industry veterans have said, and that’s led to programs from BayBio, the region’s biotech industry trade group, including the Bay Area BioEconomy Initiative.